One client had no trouble relaxing her body, but her mind was continually racing with questions of how, why, what does this mean, is this real, etc. Every time a past life image would begin to emerge for her, it would freeze frame or disappear as we tried to move forward. Another client was so worried about not wanting to 'make it up' that she couldn't even relax enough to imagine being in a beautiful, peaceful setting.
I always advise clients in advance that the best way to facilitate their past life recall is to just take whatever comes up at face value - at least during the session. Treat it like a story we're exploring, don't worry about if it's "real" or where the story came from. It's surprising how clients who feel like they're making it up suddenly are immersed in a story that has huge emotional content for them and which speaks directly to current issues in their lives. And who knows where imagination comes from anyway? Could be a past life bleeding through!
Holding it lightly, being in the experience rather than standing on the outside trying to analyze and make sense of it, leads to the most success. That's probably true of life in general!